Gypsum product and method therefor

ABSTRACT

A method for making a gypsum product water resistant, the method comprising adding a suspension of a hydrophobic substance to a gypsum slurry.

FIELD OF THE INVENTION

[0001] The present invention relates generally to gypsum products, andparticularly to a method and system for making a gypsum product waterresistant, such as with the addition of a suspension into the productionline of the gypsum product.

BACKGROUND OF THE INVENTION

[0002] Gypsum (calcium sulfate dihydrate or hemihydrate) is a well-knownmaterial used in making industrial and building products, especiallygypsum wallboard. It is a plentiful and generally inexpensive rawmaterial, which, through a process of hydration may turn into slurry,which may be cast, molded or otherwise formed to useful shapes, anddried to a final product. Gypsum wallboard generally consists of arehydrated gypsum core sandwiched between multi-ply paper cover sheets,and is used largely for interior wall and ceiling applications.

[0003] However, gypsum products, e.g., wallboard, tile, block, casts andthe like, have relatively little resistance to water. When ordinarygypsum wallboard, for example, is immersed in water, the board mayquickly absorb a considerable amount of water, lose a great deal of itsstrength, and distort or swell in different places. Many attempts havebeen made in the past to improve the water resistance of gypsum productsby adding waterproofing materials within the gypsum slurry. The mostcommon waterproofing material in use today is a hydrophobic emulsion,usually an emulsion of wax, paraffin, asphalt or a silicone compound,e.g., silanes and siloxanes.

[0004] It is important to define clearly the difference between anemulsion and a suspension. An emulsion is defined as a dispersion of oneliquid in a second immiscible liquid. One well-known example of anemulsion is milk; another is certain kinds of paint. A suspension, onthe other hand, is defined as a dispersion of fine solid or liquidparticles in a fluid (liquid or gas), the particles being supported bybuoyancy.

[0005] Some emulsified silicone compositions used to make gypsumproducts water repellent may contain an emulsion of polysiloxane andsome parts by weight of a liquid suspension of colloidal silica andother parts by weight of an emulsifier stabilizer. However, the siliconecomposition that is actually added to the gypsum slurry is an emulsion,not a suspension.

[0006] Other methods have been proposed in the prior art to improve thewater resistance of gypsum products by coating the finished gypsumproduct with water resistant films or coatings. Another method involvesspraying molten paraffin, wax, asphalt, and the like, into the aqueousgypsum slurry.

SUMMARY OF THE INVENTION

[0007] The present invention seeks to provide an improved gypsum productand process therefor. In the present invention, contrary to the priorart, the gypsum product is made by adding a suspension of a hydrophobic(that is, water repelling or resisting, the terms being usedinterchangeably) substance, such as but not limited to, paraffin, waxand the like. Adding a hydrophobic suspension to the gypsum slurry mayprovide several advantages Emulsions have to be stored at the site wherethe gypsum product is produced, and have a limited shelf life. Themanufacture of emulsions uses a lot of energy and is relatively costly.In contrast, the raw materials for making the suspension are muchcheaper and are much more stable. Production of certain water repellentsuspensions requires heat. The suspension may be manufactured at thesite where the gypsum product is produced. The excess heat of the gypsumproduction process may be used as part of the manufacturing process ofthe suspension. Making the suspension at the site where the gypsumproduct is produced, and introducing the suspension on-line to thegypsum slurry, may provide significant savings in energy, storage,manpower, etc.

[0008] There is thus provided in accordance with an embodiment of thepresent invention a method for making a gypsum product water resistant,the method comprising adding a suspension of a hydrophobic substance toa gypsum slurry.

[0009] In accordance with an embodiment of the present invention thesuspension is added to the gypsum slurry on-line at a production linewhere a gypsum product is produced.

[0010] Further in accordance with an embodiment of the presentinvention, the hydrophobic substance may be stored in a first storagecontainer, a liquid may be stored in a second storage container, and thesuspension may be formed by dispersing the hydrophobic substance in theliquid in a mixing device.

[0011] Still further in accordance with an embodiment of the presentinvention the suspension may be added directly from the mixing device tothe gypsum slurry.

[0012] In accordance with another embodiment of the present inventionthe suspension may be fed from the mixing device to an auxiliary mixingdevice, and the suspension may be added from the auxiliary mixing deviceto the gypsum slurry.

[0013] Further in accordance with an embodiment of the present inventionthe flow of the suspension to the gypsum slurry may be controlled with acontrol feeder valve.

[0014] Still further in accordance with an embodiment of the presentinvention the suspension may be added to the gypsum slurry in aproduction line, and the production line and the control feeder valvemay operate in a closed control loop.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will be understood and appreciated morefully from the following detailed description taken in conjunction withthe drawing in which:

[0016]FIG. 1 is a simplified block diagram of a method and system formaking a gypsum product water resistant, in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] Reference is now made to FIG. 1, which illustrates a method andsystem for making a gypsum product water resistant, in accordance withan embodiment of the present invention.

[0018] A hydrophobic substance 10, such as but not limited to paraffin,wax, asphalt and the like or any combination thereof, may be stored in astorage container 12. Hydrophobic substance 10 may be in the form ofliquid, particles, flakes, pellets and other shapes, of any size.Storage container 12 may comprise a mixer 14. Dispersing aids (notshown) may be added to hydrophobic substance 10 in storage container 12.Mixer 14 may be used to reduce hydrophobic substance 10 to particles ofany desired size. Provision may be made for controlling the temperatureof the contents of storage container 12, such as, but not limited to, toa temperature range of 60-98° C.

[0019] Another storage container 16 may be provided for storing thereina liquid 18, such as but not limited to, water, which will be used todisperse therein hydrophobic substance 10 to form a suspension. Storagecontainer 16 may also comprise a mixer 20. Dispersing aids (not shown)may be added to liquid 18 in container 16. Provision may be made forcontrolling the temperature of the contents of storage container 16,such as, but not limited to, to a temperature range of 60-98° C.

[0020] The contents, or any portion thereof, of storage containers 12and 16 may be fed via tubing 22 and 24, respectively, to a batch mixingdevice 26, where hydrophobic substance 10 is dispersed in liquid 18 toform a suspension 27. Control valves 28 and 30, respectively, maycontrol the flow of material from storage containers 12 and 16 to batchmixing device 26. Batch mixing device 26 may comprise a mixer 32, whichmay be any suitable dispersing mixer, such as but not limited to, apropeller, a stirrer, or dissolver moving at any suitable rate to formor maintain suspension 27. A control unit 34 may be provided thatcontrols operation of batch mixing device 26, such as but not limitedto, the weight or volume of the substances being mixed, the pressure ortemperature of batch mixing device 26, and the time duration of mixing.Dispersing aids (not shown) may be added to the suspension in storagecontainer 26. Provision may be made for controlling the temperature ofthe contents of storage container 16, such as but not limited to, to atemperature range of 60-98° C.

[0021] Suspension 27 may be added directly, if desired, from batchmixing device 26 to a gypsum slurry mixer 41. Gypsum slurry 40 may flowalong a production line 42 for making a gypsum product 44, such as butnot limited to, pre-cast gypsum products, e.g., wallboard, tile, block,casts and the like. The addition of suspension 27 may impart waterresistance to the final gypsum product 44. The amount of suspension 27added to gypsum slurry 40 and the rate of its addition thereto may befunctions of various factors, such as but not limited to, the speed ofthe production line 42, the type of the gypsum product, the desiredquality or thickness or other property of the product, the ratio ofhydrophobic substance 10 to liquid 18 in suspension 27, etc. A controlprocess feeder valve 50 may control the flow of suspension 27 to thegypsum slurry mixer 41 in production line 42. The production line 42 andcontrol process feeder valve 50 may operate in a closed control loop,wherein the rate of production line 42 automatically controls thefeeding of suspension 27 to gypsum slurry mixer 41.

[0022] Instead of adding suspension 27 directly from batch mixing device26 to gypsum slurry 40, suspension 27 may first flow from batch mixingdevice 26 to an auxiliary mixing device 46 via tubing 48. A controlbatch feeder valve 50 may control the flow of material from batch mixingdevice 26 to auxiliary mixing device 46. Auxiliary mixing device 46 mayalso comprise a mixer 52, which may be any suitable dispersing mixer,such as but not limited to, a propeller, stirrer, or dissolver moving atany suitable rate to form or maintain suspension 27. Provision may bemade for controlling the temperature of the contents of storagecontainer 16, such as but not limited to, to a temperature range of30-98° C. A control unit 54 may be provided that controls operation ofauxiliary mixing device 46, such as but not limited to, the weight orvolume of the substances being mixed, the pressure or temperature ofauxiliary mixing device 46, and the time duration of mixing. A controlprocess feeder valve 56 may control the flow of suspension 27, viatubing 58, to the gypsum slurry mixer 41 in production line 42. Theproduction line 42 and control process feeder valves 50 and 56 mayoperate in a closed control loop, wherein the rate of the productionline 42 automatically controls the production and feeding of suspension27 to gypsum slurry mixer 41.

[0023] It is noted that any of the mixing devices (e.g., “batch” or“auxiliary”) may comprise provision for mixing discrete batches orcontinuous mixing of substances.

[0024] It will be appreciated by person skilled in the art that thepresent invention is not limited by what has been particularly shown anddescribed herein above. Rather the scope of the present invention isdefined only by the claims that follow:

What is claimed is:
 1. A method for making a gypsum product waterresistant, the method comprising: adding a suspension of a hydrophobicsubstance to a gypsum slurry.
 2. The method according to claim 1,wherein said suspension is added to said gypsum slurry on-line at aproduction line where a gypsum product is produced.
 3. The methodaccording to claim 1, wherein said suspension is manufactured at a sitewhere the gypsum product is produced.
 4. The method according to claim3, wherein excess heat of producing the gypsum product is used as partof manufacturing said suspension.
 5. The method according to claim 1,further comprising storing said hydrophobic substance in a first storagecontainer, storing a liquid in a second storage container, and formingsaid suspension by dispersing said hydrophobic substance in said liquidin a mixing device.
 6. The method according to claim 1, wherein saidsuspension is added directly from said mixing device to said gypsumslurry.
 7. The method according to claim 1, wherein said suspension isfed from said mixing device to an auxiliary mixing device, and saidsuspension is added from said auxiliary mixing device to said gypsumslurry.
 8. The method according to claim 6, further comprisingcontrolling flow of said suspension to said gypsum slurry with a controlfeeder valve.
 9. The method according to claim 7, further comprisingcontrolling flow of said suspension to said gypsum slurry with a controlfeeder valve.
 10. The method according to claim 8, comprising producingand adding said suspension to said gypsum slurry in a production line,wherein said production line and said control feeder valve operate in aclosed control loop.
 11. The method according to claim 9, comprisingproducing and adding said suspension to said gypsum slurry in aproduction line, wherein said production line and said control feedervalve operate in a closed control loop.
 12. The method according toclaim 1, further comprising preparing the hydrophobic suspension at thegypsum production line.
 13. The method according to claim 2, furthercomprising preparing the hydrophobic suspension at the gypsum productionline.
 14. The method according to claim 1, further comprising storingsaid hydrophobic substance in a first storage container, storing aliquid in a second storage container, and forming said suspension bydispersing said hydrophobic substance in said liquid in a mixer.
 15. Themethod according to claim 2, further comprising storing said hydrophobicsubstance in a first storage container, storing a liquid in a secondstorage container, and forming said suspension by dispersing saidhydrophobic substance in said liquid in a mixer.
 16. The methodaccording to claim 6, further comprising controlling production of saidsuspension to said gypsum slurry with a control feeder valve.
 17. Themethod according to claim 7, further comprising controlling productionof said suspension to said gypsum slurry with a control feeder valve.